General information about the launch is here:
https://www.nasa.gov/mission/nasas-spacex-crs-29/
And there are a bunch of places to watch a live stream of the launch, including (but not limited to):
https://www.nasa.gov/nasatv/
https://www.youtube.com/live/Hgj1byn08lM
https://plus.nasa.gov/scheduled-video/coverage-of-the-launch-of-the-spacex-29-cargo-dragon-resupply-craft-to-the-international-space-station/
It sounds like coverage should start at 8 pm EST with the launch nominally scheduled for 8:28 EST, though I assume updated information will be posted at the CRS-29 page linked above if plans change.